This is somewhat of a common problem and tends to be more common on the eariler trucks that have a softer output shaft.
From the factory, the shift hub and the matching shift collar have a 2 degree taper that helps lock the t/case in gear.
After thousands of miles in 2 wd, and then shifting into 4wd, the worn hubs were mated to the unused 4wd hub.
This can result in a "locked in " condition which can usually be unlocked by shifting into reverse and working the clutch untill the hubs free up.
Mine has been doing this alot lately. Hard to shift out of 4wd after wheeling. I have to really smack the shifter (top shift) with my hand to get it to move, then it kinda pops out of 4wd into 2wd. Feels like it has preload of some kind on it. I tried to unload it in reverse and that does seem to help, but it is still hard to shift out of 4wd. Is there a way to fix this, seems like I've had three Toys that have done this same sort of thing... At first I thought that my front diff or axles were binding up causing alot of tension on something the t-case, but I guess, accordng to what you said, that it is definately a transfer case issue??